The ability of the auditory system to follow and to resolve changes in the amplitude and frequency of sound is of crucial importance for auditory perception and communication. This proposal focusses on amplitude changes and is a comprehensive psychophysical study of the ability to resolve and to extract information from changes in the amplitude of sound. The proposed projects are concerned with increasingly complex aspects of such dynamic processing. The objectives of these projects are: (1) to understand how amplitude changes are discriminated and coded, and how such discrimination relates to the detection of continuous amplitude changes produced by sinusoidal amplitude modulation; (2) to address fundamental questions of how auditory frequency analysis and spectral frequency region determine and affect temporal processing of amplitude changes; (3) to determine and describe how the ability to detect certain amplitude periodicities is affected by the presence of other periodicities; (4) to describe cross-channel temporal resolution, specifically, the ability to resolve differences in amplitude changes that occur in different frequency regions or channels; (5) to evaluate the hypothesis that auditory frequency selectivity 'sharpens' during stimulation and to pursue both experimentally and theoretically the implications of such dynamic filtering for dynamic processing. This project will provide information of fundamental importance for describing and understanding the dynamic properties of normal human hearing and, eventually, for understanding the consequences of hearing impairment on these properties. This project will provide normative data for evaluating the effects of hearing impairment on dynamic processes and, more generally, will provide a basis for the design of dynamic processing schemes in prosthetic devices such as hearing aids and cochlear implants.